The Utilization of Coconut Water as Medium for Rhizobia

Abstract

Coconut water (CW) was obtained from matured nuts and used as culture medium for rhizobial isolates C11, C4 from Centrosema pubescens; L15, L5 from Leucaena leucocephala; M5, M4 from Vigna radiata (mungbean); P7, P3 from Arachis hypogaea (peanut) and S38, S13 from Glycine max (soybean). Growth responses of these isolates in CW media, yeast extract mannitol broth (YEMB) and basal medium (BM) were determined after 4 days incubation at 30°C. The CW media were: aseptically collected CW (aseptic CW), original pH 5.4, aseptic CW, adjusted pH 7; sterilized CW (121°C at 15 psi for 18 min), pH 5.4, sterilized CW, pH 7.0; CW + NH4C1 (50 mg/ 100 ml), pH 5.2; and CW + K2HP04 (100 mg/100 ml), pH 6.0. Growth responses were rated according to optical density at 420 nm as follows: >1.0 = 4; 0.7 to 0.9 = 3; 0.4 to 0.6 = 2; 0.1 to 0.3 = 1; <0.1 = poor growth. All isolates scored 4 in CW media except C4, M5 and P7 which have slightly lower growth (3) in sterilized CW. Growth responses in YEMB ranged from 2 (C4, M5, P3) to 4 (L5, L15, P7) and in BM from 1 (C4, C11, M4, M5, P3, S38) to 4 (L5, L15, P7).